some explanation for PicoDiagnostics

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some explanation for PicoDiagnostics

Postby eric989 » Thu Nov 29, 2012 9:02 am

This is Eric Chen at Hongke from the other side of the world, China. I wrote this for my customers in my world. They don’t have a good understanding for PicoDiagnostics software and because Pico is improving it and add some new features usually, they may ask any kinds of questions. For them taking good advantage of PicoScope and fixing cars, I wrote this article for them. Posted it here, just in case that I misunderstand this software, someone can point it out and give me some advices. Many thanks advanced.

PicoDiagnostics software is a bright spot for PicoScope. After it released, most technicians love it, because it’s an easy and quick operating, and the result report is easy to understand. Even cars owners without technical knowledge, can read the report and know their car have a fault or not. It is very valuable for workshop/garage. When cars come in, give them a quick test, if there is something suspected, keep the cars and make a further check, maybe with PicoScope 6 Automotive software. It maybe help you find out a potential fault, then can improve your customers satisfaction; and also it is a chance to make money in other side.

1.Cylinder balance

The cylinder balance test is measures each cylinder contribution. It capture the AC ripple from battery positive/ negative terminals for analyzing. For test going well, make sure alternator in good condition, and switch on some load, such as headlight, rear demister.

All we know that vehicle is a complex system, it contribute well or not, depends on but not only cylinder compression, fuel injection, ignition.

Cylinder test is a relative test, it labeled the best contribution cylinder as 100%. But it doesn’t mean the contribution of the cylinder labeled with 100% doesn’t change. Why always labeled with 100%, that is because it always contribute most compared with other cylinders.

Some customers said that at a certain moment, the software show one cylinder have a worst misfire, then the bar for contribution should be shortest. It is not correct. I want to explain with some figures.

Figure A is a cylinder balance test report for a 4 cylinders car.

Pic1.jpg


Figure A : at this moment, each cylinder’ contribution and misfire situation as follow:
A cylinder contribute most, labeled with 100%; misfire is 21.4% (3/14)
B cylinder’s contribution is 97% of A cylinder’s ; misfire is 35.7% (5/14)
C cylinder’s contribution is 95% of A cylinder’s; misfire is 42.8%(6/14)
D cylinder’s contribution is 79% of A cylinder’s; misfire is 0 (0/14)

The green bar for 100%、97%、95%、79% , is the live contribution for the certain moment; if one cylinder’s contribution compared with other cylinder’s is changing, then the percentage for the green bar is changing accordingly.

The bar aside the contribution bar is indicate misfire situation, and use with different colors for misfire levels. The color is more dark, misfire is more serious. The denominator of 3/14(5/14 、6/14、0/14)is total engine cycles; the numerator is total misfire number. The denominator accumulate when engine rotate; the numerator accumulate when misfire occur.

Misfire is said the fuel burning is faulty(maybe burn line isn’t good, HT volt is too low etc. ). But it doesn’t mean that spark plug doesn’t fire. So if one cylinder have a misfire, it still contribute for engine power.

As mentioned above, there are many factors affect cylinder contribution. If a cylinder have a most serious misfire, it maybe not the cylinder which contribute the least.

Need to note that: the contribution bar is for a certain moment; the misfire bar is for total time from start to the viewing moment.

Pic2.jpg


Figure B : at this moment, each cylinder’ contribution and misfire situation as follow:
A cylinder contribute most, labeled with 100%; misfire is 3.6% (10/274)
B cylinder’s contribution is 97% of A cylinder’s ; misfire is 13.1% (36/274)
C cylinder’s contribution is 93% of A cylinder’s; misfire is29.9% (82/274)
D cylinder’s contribution is 82% of A cylinder’s; misfire is 4.7% (13/274)

Figure A and B are from the same test, but at different time.

Pic3.jpg


Figure C is from another car. at this moment, each cylinder’ misfire situation as follow:
Cylinder A: 106/1642,
Cylinder B: 75/1642,
Cylinder C: 280/1642,
Cylinder D: 62/1642

(This is from Pico’s video https://www.picoauto.com/video/misfire-diagnosis.html)

In figure C we can see that the cylinder C’s contribution is 10%. Disconnected the cylinder C’ fuel injection. But why its contribution is 10% not 0, that it’s because the cylinder C just like a air spring, it will force back after being compressed.

Sorry, the figure is not clear.

Pic4.jpg


Figure D :reconnected cylinder C’s fuel injection. At this moment each cylinder’ misfire situation as follow:
Cylinder A: 144/2203,
Cylinder B: 102/2203,
Cylinder C: 762/2203,
Cylinder D: 88/2203

We can see that the cylinder C’s contribution is very good (99%) at that certain moment. But it had a more serious misfire (762/2203)than other cylinders.

2.Compression test

There is very few question about this test. Also it detect voltage fluctuation between battery positive/negative terminals to judge compression situation. As we known, whe we crank the engine, the more sealed the cylinder have, the more voltage consume for the cylinder; and vice versa. The we can judge the seal of cylinder by voltage drop.

Pic5.jpg


3.Battery test

The key thing for this test is inputting correct parameters for battery . According to IEEE standard 1188-1996 (hope that I remember right ), battery’s capacity below 80% shows that the battery rate of deterioration is increasing even if there is ample capacity to meet the load requirements, the battery should be replaced. The capacity is measured by Cold Crank Amp, abbreviate to CCA. There are several standard for battery capacity such as SAE, DIN, EN, CCA, JIS.

Pic6.jpg
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For accurate test, please remember input a correct standard and a correct capacity for the battery. A rule is inputting what labeled on battery. Currently, PicoDiagnostics have three standards(DIN,SAE,EN) for us. I assume Pico will increase more standards for users.

Pic7.jpg
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The ambient temperature and battery type are also important. Don’t make it wrong.

Pic8.jpg
Eric Chen
Hongke Technology,China
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Re: some explanation for PicoDiagnostics

Postby LucaB » Tue Dec 04, 2012 11:05 pm

Hi, How can we understand what is 1 ° - 2 ° - 3 ° -4 ° cylinder?
Sorry for my bad English
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Re: some explanation for PicoDiagnostics

Postby eric989 » Thu Dec 06, 2012 3:54 am

LucaB wrote:Hi, How can we understand what is 1 ° - 2 ° - 3 ° -4 ° cylinder?
Sorry for my bad English

briefly disable one cylinder,unplug its injector maybe, you will see one bar drop down. Then you know the bar represents the cylinder you disable. And the rest bars are just in firing order.

My English is bad too, haha.
Eric Chen
Hongke Technology,China
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